Reactions for Polyurethane Identification

These have the advantage of being quick and relatively cheap to perform requiring no complicated instrumental procedures. 

This test identifies the presence of esters, and if the test is negative the assumption is made that a polyether is present. The test is based on the reaction of the ester with hydroxylamine, with the formation of the hydroxamic salt and the subsequent reaction with acidic ferric chloride to give a complex salt possessing an intense violet or purple colour. 

Approximately 50 mg of the polymer are cut into small pieces and reacted with a few drops of 2n potassium hydroxide in methanol plus phenolphthalein. The mixture should be kept alkaline as indicated by the phenolphthalein. A few drops of a saturated solution of hydroxylamine hydrochloride in methanol are added and the mixture heated to a maximum of 50°C for a few seconds. The mixture is then acidified with In hydrochloric acid and one drop of a 3% solution of ferric chloride in water 

For highly crosslinked polymers it is desirable to heat the mixture for 20-40 s in order to increase the reactivity. 

Esters present as solvents, plasticizers, etc., interfere. The functional groups possibly forming during urethane formation, which have been pointed out previously, do not interfere with the colour test under the test conditions. Ethers do not give the characteristic colour reaction. 

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